1. Field of the Invention
The present invention relates to polymeric metal complex compositions comprising metallic complexes covalently bound to conjugated polymers. The invention further relates to electronic devices in which the active layer includes such polymeric metal complex compositions.
2. Description of the Related Art
Organic electronic devices that emit light, such as light-emitting diodes that make up displays, can be used in many different kinds of electronic equipment. In all such devices, an organic active layer is sandwiched between two electrical contact layers. At least one of the electrical contact layers is light-transmitting so that light can pass through the electrical contact layer. The organic active layer emits light through the light-transmitting electrical contact layer upon application of a voltage across the electrical contact layers.
It is well known to use organic electroluminescent compounds as the active component in light-emitting diodes. Simple organic molecules such as anthracene, thiadiazole derivatives, and coumarin derivatives are known to show electroluminescence. Semiconductive conjugated polymers have also been used as electroluminescent components, as had been disclosed in, for example, Friend et al., U.S. Pat. No. 5,247,190, Heeger et al., U.S. Pat. No. 5,408,109, and Nakano et al., Published European Patent Application 443 861. Polymeric materials with stilbenyl or oxadiazole side chains have been reported by Holmes et al., U.S. Pat. No. 5,653,914. Complexes of 8-hydroxyquinolate with trivalent metal ions, particularly aluminum, have been extensively used as electroluminescent components, as has been disclosed in, for example, Tang et al., U.S. Pat. No. 5,552,678. Complexes of Iridium with phenylpyridine, phenylquinoline, or phenylpyrimidine ligands have been disclosed as electroluminescent compounds in Petrov et al., Published PCT Application 02/02714.
Electroluminescent devices with an active layer of polyvinyl carbazole (PVK) doped with metallic complexes of iridium have been described by Burrows and Thompson in published PCT applications WO 00/70655 and WO 01/41512. Electroluminescent emissive layers comprising a charge carrying host material and a phosphorescent platinum complex have been described by Thompson et al., in U.S. Pat. No. 6,303,238, Bradley et al., in Synth. Met. (2001), 116 (1–3), 379–383, and Campbell et al., in Phys. Rev. B, Vol. 65 085210.
Small molecule light-emitting materials are usually deposited by evaporative techniques. The equipment required for such processes can be quite expensive and may not be adaptable to continuous processing. Small molecule light-emitting materials can be coated from solution. However, they have a tendency to crystallize with evaporation of the coating solvent, which reduces their electroluminescent effectiveness.
There is a continuing need for electroluminescent materials having improved electrical efficiency.